Such microscopes are often embodied as stereomicroscopes, in particular as surgical microscopes. DE 103 25 575 A1 (corresponds to U.S. Pat. No. 7,057,807) discloses a microscope of this kind for simultaneous observation of a specimen by a first and a second observer, the microscope comprising deflection elements for deflecting an observation beam path, which proceeds parallel to the optical axis of the main objective, into a first plane that extends substantially perpendicular to the aforesaid optical axis, and then into a second plane that is substantially parallel to and above the first plane. Devices are also provided for coupling out the observation beam path for the observers. In this microscope, there is provided between the main objective and the first plane an illumination unit that generates an illumination beam path which is guided through the main objective of the microscope. An advantage of this shared utilization of the main objective for the illumination and observation beam paths is that upon a change in the focal length of the main objective, a separate adaptation of the illuminated field to the changing field of view is not necessary. On the other hand, the illumination unit to be accommodated between the main objective and said first plane requires space that increases the overall physical height of the microscope. The distance between the main objective and the first deflection element that deflects the observation beam path into the first plane should, however, be kept as small as possible for optical reasons, for example because of vignetting and reflections.
A stereomicroscope configuration that is similar in terms of the arrangement of the illumination unit in the microscope is known from US 2001/0010592 A1. With the configuration described therein, connection of an assistant's microscope allows specimen observation by a total of three observers. Here as well, a microscope configuration of the least possible vertical height is to be implemented. Here the illumination unit is located at the height of the main objective and next to it, below a first plane in which the observation beam path, after the first deflection thereof by a first deflection element, proceeds behind the main objective of the microscope.